Thermo Scientific™ mCP Selective Agar

In mCP Medium, lack of b-D-glucosidase activity (an enzyme involved in cellobiose fermentation), fermentation of sucrose, and production of acid phosphatase are used to differentiate presumptive Clostridium perfringens colonies from other Clostridium spp. Lack of β-D glucosidase activity means that Clostridium perfringens does not cleave the chromogen, indoxyl β-D glucoside, in the medium. Furthermore, as the organisms ferment the sucrose in the medium, reducing the pH, bromocresol purple changes from purple to yellow. This results in characteristic opaque yellow Clostridium perfringens colonies. Most other Clostridium spp. will appear as either purple colonies, due to the lack of sucrose fermentation, or blue/green colonies where the organism is still cleaving Indoxyl b-D glucoside and also fermenting sucrose. 

Presumptive positive Clostridium perfringens colonies can be further tested for acid phosphatase activity by exposure to ammonium hydroxide vapour for 20 to 30 seconds. Clostridium perfringens colonies turn pink or red as phenolphthalein diphosphate is cleaved by acid phosphatase. No color change will be seen with colonies of organisms that do not posses acid phosphatase. It is important this further test is carried out as there are a very small number of non-perfringens clostridia that produce yellow colonies; however, these colonies will remain yellow after exposure to ammonium hydroxide as they are acid phosphatase-negative.

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